This research program is designed to characterize specific processes that are used in the later ("higher") stages of visual object recognition. Adult patients with focal brain damage will be tested on four types of visual tasks: 1. The selection and focus of visual attention over space. 2 . The recognition and encoding of object properties (particularly shape). 3 . The encoding of spatial properties (location, orientation, and size), and 4. The use of stored visual information to guide top-down search. A deficit will be assessed by comparing the relative differences in response times and error rates in each task for patients with the corresponding differences for age-, sex-, and education-matched normal control subjects. The hypotheses to be tested are based on a computational analysis and a computer simulation model previously developed by the researchers. Behavioral deficits will be correlated with the location of lesions as defined by MRI neuro-imaging studies.